Insulation



w. T PEIRcE INSULATION April 16,1935.

Filed Oct. 7, 1932 196099150 W44 TEE 7' PE/ECE,

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Patented Apr. 16, 1935 UNITED STATES PATENT OFFICE INSULATION Walter T. Peirce, Worcester, Mass., assignor to The American Steel and Wire Company of New Jersey, a corporation of New Jersey Application October 7, 1932, Serial No. 636,726

2 Claims. (01. 173-264) This invention relates to electrical insulation that even though all interstices are completely constructions and particularly to those characimpregnated the difierent dielectric constants of terized by laminated dielectrics arranged with oil and paper may result in relatively large pomore Or less adjacent edge portions. One object tential diiferences occurring at points which inis to improve the breakdown characteristics of troduce stresses parallel to the wound insula- 5 such constructions. tions surfaces.

In the accompanying drawing- Figure 2 illustrates a construction which di- Figure 1 is a longitudinal cross-section of a minishes the foregoing trouble to a great degree. commonly used cable insulated by a laminated This construction shows the same conductor I dielectric. insulated by oil impregnated paper tape 2 over Figure 2 is a longitudinal cross-section of a which is applied the lead sheath 3. It will be obspecific form of the present invention. served that here the paper tape tapers to a point Figure 3 is a modification of Figure 2, and at each of its edges. Such tape may be manu- Figures 4 and 5 illustrate enlarged sections of factured by calendering its edges. It is applied the dielectrics shown in the first and second figso that the enlarged tape bodies of each succesures respectively. sive layer overlie the reduced edge portions of Figure 1 shows an electric conductor I inthe one beneath, whereby the interstices or voids sulated by spirally wound paper strip layers 2 are reduced to such a minimum that the probwhich areimpregnated with oil and covered by ability of the described breakdown will be almost a lead sheath 3. The impregnating oil is supinconsequential. Also, the tangential stresses posed to completely fill all interstices between remaining will be spread over the whole width the paper strip. Actually, however, unimpregof the tape rather than concentrated at the hated areas sometimes exist between adjacent edges. edges of the tape convolutions. A still further feature lies in the fact that it In the drawing, which is illustratively exagis possible to apply the tape with lapped convolugerated, a line A-A is drawn through such an tionsand thereby secure a greater baffling action unimpregnated area. This means that there is without seriously impairing the sables flexible an air space between the tape convolutions whose characterstic. Such a construction is illustrated edges are adjacent this line. Asecond line B-B by Figure 3. This last figure shows the lead is drawn through a tape convolution whose edge sheath 3 eliminated and a fabric covering 3 subis adjacent this air space. Both of these lines stituted. indicate stress paths from the conductor l to As shown particularly well by Figure 5, the the lead sheath 3 which is assumed to be tape v2 tapers from its central portion to its grounded. In case the sheath 3 were non-conpointed or sharpenededgessyrmnetricallyrespectducting they would indicate paths to an external ing its center line so that these edges are at the o d J' latter, and its surfaces are smoothly and evenly The ne Passes through p p a a d curved. This tape is wound over the conductor l oil wh e t line pa o y through Paper in layer form with the respective edges of its and oil. This means that there will be a potenlaterally adjacent convolutions in mutually tial diiference between the two lines which will posed alinemem, as Shown by Figures 2 and 40 set up tangential stresses therebetween. That is The oil impregnation fins the interstices between to say, the potential diiferences between the exthe tape as much. as is possible.

tremes of the air gap cut by the line A-A greatly exceed those on the sides of the strip cut by It m be seen a the ventmn pnmanly the line B B because of their respectively embodies the use of dieelectrics which have edge f t dielectric constants In the case of portions of less cross sectional area than their 4., tively large voltages this ratio may increase rapidcentral P0111011, f @Speclally pp t0 ly as the result of the airs ionization. Once an a Where the dlelectrlcs have different is begun the cable rapidly deteriorates Clfic inductance capaclties. Preferably the edges throughout a constantly enlarging area are rather sharp although a somewhat more oval t i11 be ee th t m breakdowns of t shape will accomplish the same results to a lesser character under discussion seem to be directly degree- In the e p Shown the pe y be the result of more or less minute air spaces. Howof y insulating material, and the Cab e as 2. ever, even in the absence of such voids a break- Whole y be Co struc ed in other forms than down may result. This follows from the fact those p fi ally shown.

sulation therefor, said insulation including dielectric tape having sharpened edges and which tapers from its central portion to its sharpened edges symmetrically respecting its center line so that said edges are at the latter, said tape being wound oversaid conductor in layer form with the respective edges of its laterally adjacent convolutions in mutually opposed alinement and having its interstices filled with a fluid dielectric as much as is possible, said tape having smoothly 10 curved surfaces.

WALTER 'r. PEIRCE. 

